Exterior doors and windows are designed with insulation, weather resistance, and aesthetics in mind. As a result, most such products are provided with a durable outer coating, such as vinyl, metal, or paint. However, difficulties may be encountered when attempting to coat or otherwise seal joints or seams between adjacent window frame components. In this regard, there exists a need to effectively seal cut and/or exposed ends of extruded window frame members and/or interfaces therebetween. When adjacent window frame members are made of plastic, sonic welding has been used to form a bond therebetween. However, room for improvement remains for both the process and the resulting product.